Rafael Nadal survived an early scare against Australian wildcard Rinky Hijikata as the four-time winner came back to reach the US Open second round.
Spain’s 22-time Grand Slam champion was stunned as his 21-year-old opponent, ranked 198th in the world, took the first set on Arthur Ashe Stadium.
But Nadal, 36, recovered to secure a 4-6 6-2 6-3 6-3 victory in New York.
Earlier, compatriot Carlos Alcaraz progressed after Argentine Sebastian Baez was forced to retire with injury.
Contesting his first US Open match since defeating Daniil Medvedev in five sets to win the tournament in 2019, Nadal fell behind when major debutant Hijikata clinched the only break point opportunity of the opening set.
The world number three was restricted to just a single hard-court outing after withdrawing from his Wimbledon semi-final against Nick Kyrgios with an abdominal injury in July, losing in three sets to Borna Coric at the Cincinnati Masters.
But he was able to restore order, turning the match in his favour before eventually ending his opponent’s stern resistance in the fourth with an exquisite forehand down the line on his fifth match point.
Hijikata received a standing ovation for his efforts, as Nadal’s bid for a record-extending 23rd major men’s singles title began.
“It has been a long wait, for some time I thought I would not be able to be back,” said Nadal, who will play Italian Fabio Fognini next.
“I didn’t play much for the last 50 days so I have to be humble and accept the process of building positive things in practice. It is a moment to survive, stay positive and accept how things happen.
“I am just enjoying the fact that I am here, and I am here to try my best every day.”
With no ranking points to defend in New York, Nadal is the best-placed of the four players who could end the tournament as the world’s top-ranked men’s player.
Another player who could finish the tournament as the world number one is Nadal’s compatriot, the 19-year-old Alcaraz.
The third seed, bidding to win his maiden Grand Slam title in New York, progressed on Tuesday after Baez was forced to retire from a thrilling meeting between two exciting talents.
Alcaraz led 7-5 7-5 2-0 when his injured opponent took the decision, having received a medical timeout at the end of a breathless second set which featured several enthralling battles.
“Nobody wants to see the match end like this,” said Alcaraz, who meets Federico Coria in round two. “Sebastian is a great player and he deserves the best things.
“It was really tough, the second set was really tough for me to stay at the level physically and mentally, but the energy I received on Arthur Ashe was really special.”
The Spaniard reached his first major quarter-final at last year’s US Open – a feat he matched at the French Open in May.
He added: “Last year was one of the best moments of my life and of my career. One year later, being fourth in the world, is something special for me.”
Elsewhere in the men’s draw, ninth seed Andrey Rublev let slip a two-set lead before prevailing in a five-set epic against Serb Laslo Djere.
The Russian eventually won 7-6 (7-5) 6-3 3-6 4-6 6-4 as he clinched his first match point on Djere’s serve after three hours and 41 minutes.
Rublev will play Kwon Soon-woo in the second round, after the South Korean defeated Spaniard Fernando Verdasco 6-2 7-6 (7-4) 6-3 6-3.
Italian Jannik Sinner, the 11th seed, almost went a break down in the final set but eventually fought his way past German Daniel Altmaier, winning 5-7 6-2 6-1 3-6 6-1.
There were no such issues for Poland’s eighth seed Hubert Hurkacz, who beat German Oscar Otte in straight sets 6-4 6-2 6-4.
Croatia’s 15th seed and 2014 champion Marin Cilic beat German Maximilian Marterer 6-3 6-2 7-5, while Bulgarian 17th seed Grigor Dimitrov won 6-3 6-2 6-2 against American Steve Johnson.
Dimitrov will face another American in Brandon Nakashima next, following the 21-year-old’s 7-6 (7-4) 6-2 6-2 win over Russian Pavel Kotov.
Another home player, John Isner, won 6-3 6-1 7-5 against Argentine Federico Delbonis and will meet Danish 28th seed Holger Rune next after the 19-year-old beat German Peter Gojowczyk 6-2 6-4 7-6 (7-5).
Canadian 19th seed Denis Shapovalov came through in five sets against Swiss player Marc-Andrea Huesler, winning 2-6 6-4 6-4 3-6 6-1, while American 22nd seed Frances Tiafoe beat compatriot Marcos Giron 7-6 (7-0) 6-4 6-3.
Fognini set up his meeting with Nadal by coming back from two sets down to win 1-6 5-7 6-4 6-1 6-4 against Russian Aslan Karatsev, and Argentine Coria faces Alcaraz following his 7-5 6-4 6-3 victory over Dutchman Tallon Griekspoor.